You will never be as young and as healthy as you are right now!
You cannot wait to buy insurance until you need it due to illness or injury.
When a dentist calls me about coverage and says, “How soon can you come to my office to write this up?” before they even ask about the price, my immediate response is, “I am guessing you recently went to see your physician; what was the diagnosis?”
I think the best time to buy is as soon as you can afford to pay for the coverage. If your insurance ever seems expensive, you probably haven’t been made fully aware of the benefits and the likelihood of a claim.